Wow! In this footage obtained from a DC-8 flying over Australia, you can see the probe breaking up, with individual pieces falling off and burning up as they ram through the Earth’s atmosphere at several kilometers per second. The last little piece you can see at the end is, I think, the hardened component that contains samples of the asteroid Itokawa, obtained when Hayabusa landed on its surface.

As I mentioned in an earlier post, Itokawa is a 500-meter-long potato-shaped rubble pile, an asteroid that is not a solid rock like a boulder or mountain, but probably an assemblage of rubble held together by its own gravity. If one of these things were headed straight for us, we could lob nukes at it, even slam it with space probes at high speed to try to push it out of the way, and it would laugh at us. We need to understand these objects much better than we currently do if the time ever comes that we need to keep one from smacking into us. The sample of Itokawa contained inside that tiny glowing dot you saw in that video may just give us some of the answers we need to do that.

Science! It makes the world better, but it also just might save it, too.

Stay tuned to Emily’s blog for more information about Hayabusa as she gets it! She has already posted some great images and video, too.

When I hit the atmosphere, I’ll burn like a meteor.
I wonder, he said, if anyone’ll see me?”

The small boy on the country road looked up and screamed. “Look, Mom, look! A falling star!”
The blazing white star fell down the sky of dusk in Illinois.
“Make a wish,” said his mother. “Make a wish.”

*whine* I thought this was supposed to be an ASTRONOMY blog, wahhh….wait a minute.

Haha, great post Phil! That video is very impressive! It’s these kinds of things that keeps me hoping for an expanded space program. It’s like, “look guys, see this thing? It could KILL US ALL. Can we please look into this?”

Wow. It is amazing that it was able to land on that tiny little mass of rubble in the first place. When you think of all the planning, building, tweaking, problem solving, time, complexity, and thousands of things not considered….It amazing that it was so successful.

It is indeed a symbol of the talent of the human species. Perhaps it will even be the key to saving the human species…

I hope there turns out to be good stuff inside. (Buttered popcorn would be nice.)

A DC-8? Goodness. I was aboard the 7th (or so) United DC-8 regular flight from New York to Los Angeles (stop in Chicago) 40 (to 43) years ago. Pilot carefully explained that the plane could reverse its two inboard engines in flight to slow down, and it was *rough* when that happened. On his prior flight, Chicago controllers forgot he was a jet, and suddenly commanded “reduce to landing speed immediately”. Scared the passengers badly.

(Mother, a physics PhD, did applied physics work on DC-6–and I think 7–before moving on to JPL.)

Thehaymarketbomber (10): I was being a little flip here; it depends on the size of the asteroid, the nuclear weapon used, and so on. In some cases, sure, a nuke will vaporize the asteroid. In others, it may vaporize the surface enough that the expanding gas will act as a rocket motor, pushing the asteroid away. On others, it simply isn’t enough to have much effect.

That asteroid really looks more like a rubble pile than a rock. Normally the pictures of asteroids we get to see are larger and I presume more influenced by gravity and impacts so that they look more like one giant rock with holes in it, rather than a mound of gravel and boulders.

Its 4.30 a.m. South Australian time now and sunrise is about 7 a.m. so there’ll be a few hours yet if they’re waiting for sunrise as suggested by (#15) AJ.

(In other news, Germany leading us 2-nil in the world cup soccer / football game. Durnnit. )

UPDATE : Half-time score still 2-0 Germany. In other sporting news : Lewis Hamilton headed a McLaren-Mercedes 1-2 in the Canadian F1 GP with Alonso’s Ferrari 3rd. Now 4.48 a.m. South Australia time. All Off Topic, I know but figure some folks here may be interested.

The most interesting scientific result (to me, so far) from Hayabusa is that Itokawa is well mixed, and apparently subject to churning of material (i.e., material from inside is brought to the surface on a regular basis). The only way I can figure out to do this without disrupting the asteroid entirely is if the rubble pile is held together by something other than just gravity, say electrostatic forces, or even Van der Waals forces (surface adhesion). Otherwise, with a surface gravity 10^18 joules (or a Gigaton of TNT or more) of kinetic energy from a Itokawa hit. (Note : Itokawa is used for illustration only; it is not on any sort of near collision course with the Earth.)

Oli @18 – we do not know if there was a sample. However, the door is supposed to have been open when the spacecraft “landed” on the asteroid. so there is a decent hope that some material was knocked loose and captured. Given what can be done with even microgram sized specks, it wouldn’t take much to provide a solid scientific return from this.

@22. Marshall – Your numbers look about right, but if we have enough time we don’t have to clobber it with so much force all at once.

I worked up the following a couple of years ago after NGT (Dr. Tyson) commented on “an asteroid the size of the Rose Bowl” that was found to be on a close-to-interception path with the Earth in about 20 years.

If we have that much time, we can use a “gravity tug.” That sounds exotic, but all it means is that you have a spacecraft hover over the body and the degree of “tug” will equal the force necessary to make it hover (essentially its weight). That infinitesimal amount of force, applied over a long period will move the body enough to miss us. Here’s how the orbital dynamics work:

Interplanetary bodies generally don’t just auger directly into the Earth on first encounter. Usually, it’s a close pass that alters the orbit of the body enough that on the next pass it hits us. Whether it hits or misses us depends on exactly where the point of closest approach is. The critical area is quite small (some 10s of Km) and is called “the slot” by orbit analyst types. To make sure that an approaching body misses us, all we have to do is keep it out of the slot on the initial pass. So “all we have to do” is move the body about 100 Km or so before the initial pass which will give us a margin of safety of about 10. To make the numbers easy, let’s say we have 10 years to do it in and that the mass of the body is 10^10 Kg.

So, according to Newton, s = .5 a*t^2 or a = 2*s/t^2
Inserting our numbers we get a = 2*10^5/(3.16*10^8)^2 = 2*10^-12 m/sec^2
In English, that’s 2 trillionths of a meter per sec^2.

The force needed to accelerate it by that much is F = ma = 10^10 * 2*10^-12 = 0.02 N
Wow, 0.02 Newtons. That amount of thrust is easily provided by an ion engine.

OK, so how big would this space tug have to be? Our buddy Isaac tells us that the gravitational force between two objects is: F= G*m1*m2/r^2 where the “m”s are the masses of the two objects, r is the distance between their centers and G is the gravitational constant. Since the spacecraft will be hovering, we know that the force will be equal to the amount of “tug” we want, which was already calculated to be 0.02N. If it hovers, say, 1 Km from the asteroid, that makes r = 1,000 m and G in these units is 6.67*10^-11. The mass of the asteroid (m1) is still 10^10 Kg, so rearranging and solving for m2 we get m2 = 2.33*10^3 Kg, or a little over two metric tonnes. That’s pretty tiny for a spacecraft of any type! We’d need a lot more mass than that just to store the reaction mass.

This sort of space tug would be pretty simple, just some station-keeping guidance once it had rendezvoused with the object. In fact, it would probably be a series of spacecraft used sequentially. Note that these will NOT be in orbit about the body. That wouldn’t produce any net force on it. Also, there would have to be at least two thrusters aimed at an angle to miss the body. Since the thrust vector has to be aimed right at the body’s CG, a single thruster would impinge on the surface negating the effect of the tug. The nice thing about a gravity tug is that it’s non-contact. You don’t have to land on the body or aim a surface-mounted rocket motor (tricky if it’s rotating) or worry about the internal structure. It’s all the same to gravity.

I have just watched the reentry on the evening news services in South Australia. Awesome video on the news. What a great story. It makes me wonder where we would be as a species if we werent so keen on killing one another.
If half of what the world spends on military hardware a year was spent on expanding into space. Where would we have gotten too already?

I hope it was meant to break apart on re-entry. The video reminds me of Columbia.

Yes, the main Hayabusa spacecraft itself wasn’t meant to re-enter our atmosphere originally but did so because of technical woes that happened along the way or so I understand. It *was* indeed expected to burn up as it did like a “shooting star”.

I wonder if any pieces of the spaceprobe survived and can be located? Haven’t heard of any yet, just curious.

(BTW. The media coverage here in South Oz has been pretty good on this actually.)

OTOH, the capsule containing the sample *was* designed for re-entry & has done so successfully parachuting down and has been picked up and taken back to Japan for analysis. Hopefully it’s got something!

As for poignant memories of Columbia, yes. We’ll always remember that and the people who flew it. But when things enter our atmosphere and break apart and burn up – well, that’s just what they look like and usually, usually, (hopefully!) its going to just be a beautiful & natural sight bringing wonder and joy not sadness. Or more than the faintest tinge of remembered sadness anyway. Those people died in a remarkable way doing what they loved. There is pain in that, yes, but also, oddly, some somber satisfaction as well. If I could choose how to go that’d be the way or at least high on the list.

And whatever happened with the US “Stardust” mission a few years back, where the parachute failed to open and the capsule crashed to the ground? Any useful information recovered from that?

Even despite Genesis spinning down and crashing into the salt flat with a thud. 😉

@39. Ken B Says:

The problem with referring to comments by their number — moderated posts that show up later will change the numbers.

True – that’s why I like to cite both the name and the comment number in the format I do here. Sometimes the same person (eg. yours truly) will post a number of times in the one thread so just using names isn’t enough and the numbering with moderation comments has the problem you mentioned.

Perhaps if the BA could arrange it so that the comments were numbered NOT in chronological order of posting but rather in order of them passing moderation here where applicable it would fix that? Dunno if it can be done though.

Usually, context and the quotes when cited enable you to know which comment / person is being referred to anyhow.

@ 40. Ray Says:

Anyone else flashing back to Andromeda Strain?

Well I live in Adelaide which is due south of the recovery area in Woomera so I should be about the first to know. If I feel like I’m mutating or falling dead from a space plague, then I’ll try to post & let you know! 😉